The invention concerns a wet clutch or a friction plate brake according to the pre-characterizing portion of Claim 1.
In this field a generic wet clutch or friction plate brake is generally comprised of a clutch housing, a clutch hub, various outer and inner friction plates, an apply piston and an apply piston support device for carrying the apply piston. All the above-mentioned construction components are as a rule formed essentially rotation-symmetrically and are provided coaxially about a common (rotation) axis.
The clutch housing is essentially in the form of a hollow cylinder and is mounted rotatably about the rotation axis. It carries one or more outer friction plates, wherein these are essentially displaceable or slideable in the axial direction.
In similar manner the clutch hub is also essentially in the form of a hollow cylinder and is mounted rotatably about the same rotation axis. This also carries one or more preferably ring-shaped inner friction plates which are displaceable essentially in the axial direction.
Outer friction plates and inner friction plates alternate in the axial direction, thereby forming so-called friction pack. Thereby one of the contact surfaces of an outer friction plate is arranged for contacting one of the contact surfaces of one inner friction plate, so that these can be brought into frictional contact by pressing against each other. The outer or the inner friction plates carry a friction lining.
The friction pack is closed off on one end in the axial direction by an apply plate, which could represent either one of the friction plates carried on the clutch housing or one of the friction plates carried on the clutch hub. In the axial direction on the other side of the friction pack there is an end plate which is basically not slideable in the axial direction. This end plate represents one of the friction plates carried on the clutch housing or one of the friction plates carried on the clutch hub.
In order to bring the broad faces of adjacent outer and inner friction plates into frictional contact with each other in the above-described manner, there is provided in accordance with the state of the art a so-called apply piston. An apply piston of this type is formed in the manner of a hollow cylinder or pot. The outer rim of the sidewall of the pot forms a ring-shaped pressure unit, which can be pressed against the free broad surface of the above-described apply plate. In this engaged or pressed-in condition, torque can be transmitted from the clutch housing onto the clutch hub, or the reverse.
In order to be able to operate this actuation piston it is necessary on the one hand that this is mounted in suitable manner to be axially slideable, and on the other hand that it can transmit a pressure force.
According to the state of the art, for transmission of the pressure force an apply piston support device is provided which is rigidly connected with the clutch hub or clutch housing by means of a suitable connecting device. This actuation piston support device is essentially in the form of a hollow cylinder and is provided coaxially and preferably radially interiorly to the clutch hub. The apply piston support device includes an essentially ring shaped piston support plate or plate, against which or upon which on one side, which in the following will be referred to as the piston support plate inner surface, the apply piston is supported for axially transmitting pressure force.
In this device, a ring-shaped hollow space is enclosed by the piston support plate inner surface, against which the apply piston supports itself, in combination with the cylindrically shaped support surface of the apply piston support device, plus the piston support outer surface of the apply piston by means of which the apply piston is supported on the piston support plate inner surface. In this hollow space, which in the following will be referred to as the apply piston space, there is situated oil, as in the entire inner space of the wet clutch.
If the clutch device is then set into rotational movement (so-called rotating clutch actuation), with increasing speed of rotation, oil tends to flow in this apply piston space due to centrifugal force and at the same time there is an associated increase in pressure. This pressure increase causes the apply piston to press in the axial direction against the friction pack. It is then necessary to employ suitable means to compensate for this parasitic force induced by centrifugal force.
According to the state of the art basically two possibilities are known for compensating for centrifugal force. On the one hand centrifugal force is compensated by a “check ball”.
This means need not be discussed in greater detail in the following. It is further known in accordance with the state of the art to employ a so-called balance or balance piston. A balance piston of this type is based upon the idea of providing, in the apply piston space lying opposite the side of the apply piston, a space filled with oil in which a counter pressure is produced due to centrifugal force. In practical terms this is realized in accordance with the state of the art in the below described mode and manner.
One such balance piston according to the state of the art is essentially in the shape of a hollow cylinder, including a ring shaped floor and a cylindrical wall. This balance piston is provided coaxially to the clutch hub and is essentially fixed in axial direction with the apply piston support device. According to the state of the art the outer wall of the cylinder is provided coaxial and radially interior to the apply piston support device, while the walls of the hollow cylindrically shaped apply piston support device as well as those of the balance piston at their base or floor surfaces are oriented opposing each other in the axial direction.
The apply piston exhibits in the coaxial arrangement a ring shaped wall, of which the outer surface is guided slideably essentially in the axial direction on the inner surface of the cylindrical wall of the apply piston support device and of which the inner surface is guided slideably essentially in the axial direction on the outer surface of the essentially cylindrically shaped wall of the balance piston. By this particular arrangement of balance piston and apply piston to each other a hollow shape is formed, which represents the above discussed equalizing space.
Although an arrangement of this type has essentially proven itself as useful, with this type of arrangement a complete compensation of centrifugal forces is only possible at great expense. Usually, return spring devices are used. Further, attempts have been made to conform the axial lengths and stroke paths of apply piston support devices, apply pistons comprised of one or more parts, and balance pistons. Through the use of further supplemental construction components, finally a complete compensation is achieved. The realization of complete compensation however requires a substantial construction investment.
It has been found, that an optimization of this type is not possible in a compact construction. Until now a compensation of approximately 80% has been achieved herein.